This invention relates generally to actuators for fluid flow control valves and in particular to electro-mechanical actuators.
A variety of fluid flow control valves and corresponding valve actuators are utilized for on/off control or throttling the flow of fluid, such as in a gas or oil pipeline system, or in other process fluid systems. The fluid flow control valves are typically sliding stem control valves or rotary action control valves and are operated by a valve actuator such as an electro-pneumatic actuator piston or diaphragm unit. In a fluid flow control situation the actuator is responding to the output of a valve positioner or valve controller instrument for accurate throttling control of the valve. Another type of actuator is an electro-mechanical valve actuator containing an electric motor, a motor control unit, and a driving gear configuration with torque limiting devices for controlling the torque applied to the valve shaft. Such an actuator can contain several options, such as speed control, a modulating unit, a position transmitter, etc.
In such process fluid systems, a variety of valve actuators, positioners, or controller instruments, etc., (hereinafter termed xe2x80x9cfield instrumentsxe2x80x9d) are connected to the pipeline system for controlling and/or responding to the fluid flow. Some of the present field instruments are so-called xe2x80x9csmartxe2x80x9d instruments containing a microprocessor so that such field instruments can be controlled from a remote location for suitably controlling the fluid flow rate, and can also provide a variety of flow characteristics as well as diagnostic information. However, the standard field instruments without microprocessors are still in substantial use and demand due to their low cost compared to a xe2x80x9csmartxe2x80x9d field instrument. Therefore, in many instances the process fluid system includes a mixture of xe2x80x9csmartxe2x80x9d field instruments as well as standard field instruments. Typically, such field instruments are connected to a bus from a controller to receive power drawn from the bus in the form of standard 4-20 ma or voltage control signals.
It is desired at times to reduce the need for large numbers of expensive, xe2x80x9csmartxe2x80x9d field instruments in such process fluid systems and instead to utilize larger numbers of standard field instruments where feasible. As an example, it would be desirable to utilize one expensive xe2x80x9csmartxe2x80x9d field instrument to control other standard field instruments, and it would be especially desirable to control other standard field instruments of different types, i.e., electro-mechanical actuators, electro-pneumatic actuators, valve controller instruments, etc., via the xe2x80x9csmartxe2x80x9d instrument. Secondly it is desired to control a variety of such field instruments without requiring the bus be connected to conventional control signals which otherwise draw a substantial amount of power from the bus which has somewhat limited power carrying capacity.
In accordance with the principles of the present invention, there is provided an electro-mechanical actuator for operating a fluid control valve and controlling the operation of one or more field instruments. In particular there is provided an electro-mechanical actuator including a drive gear having an output coupled to another electro-pneumatic or electro-mechanical actuator. A control unit is coupled to a power source and supplies the open and close power levels in the form of control signals to the electric motor for opening and closing the valve. The control unit includes auxiliary inputs and outputs to control the operation of one or more other field instruments.
The auxiliary control output of the electro-mechanical actuator of the present invention may be connected to a standard electro-mechanical actuator for on/off control of the associated fluid control valve. In addition, the auxiliary control output can be coupled to an electro-pneumatic positioner for activating the positioner and providing suitable on/off controls to correspondingly open and close the associated fluid control valve.
In addition, respective close and open sensors may be provided for monitoring the close and open conditions of the field instruments and providing a suitable signal indication thereof. A personal computer or other host computer is connected to the electro-mechanical actuator of the present invention and can be used to not only control this first electro-mechanical actuator, but through suitable auxiliary control signals from the first electro-mechanical actuator to on/off control a second electro-mechanical actuator as well as an electro-pneumatic positioner or other type of field instrument. Accordingly, respective close and open limits devices for each of the field instruments provides the opened/closed position of the associated valve through the first electro-mechanical actuator to the personal computer or host computer.
The present invention thereby provides a significant advantage in enabling a first electro-mechanical actuator having the ability to provide auxiliary control signals for actuating other field instruments.
The features of this invention which are believed to be novel are set forth with particularity in the appended claims. The invention may be best understood by reference to the following description taken in conjunction with the accompanying drawings, in which like reference numerals identify like elements in the several figures and in which:
FIG. 1 is a schematic block diagram illustrating an electro-mechanical actuator according to the present invention utilized in a process fluid system having a variety of field instruments; and
FIG. 2 is a schematic block diagram illustrating the auxiliary control signal lines provided by the electro-mechanical actuator of FIG. 1 in response to a personal computer or host computer for controlling at least two other field instruments and auxiliary travel input lines for monitoring the limit open and limit closed travel positions of the other field instruments.